unfortunately we cannot make assumptions in Thailand because every government agency has their own interpretation of the law. Good luck and I hope you get your visa.
If you are staying with your son have him do a TM 30 showing that you live with him. Having a Non O visa already should make it easier to get a bank account. Just make sure you get a Certificate of Residency from Immigration when the TM 30 is approved.
Everyone just needs to read the Double Tax Agreement between your own country and Thailand. For US Citizens I know for sure Social Security and any other Federal Pensions are not, I repeat not taxable in Thailand.